Method and device for optical detection of substances in a liquid or gaseous medium

ABSTRACT

The invention relates to a device for optical detection of substances in a liquid or gaseous medium, with a substrate with molecules for detecting the substances that are to be detected, wherein these molecules are immobilised at a surface of the substrate or in the substrate and wherein the substances that are to be detected can essentially be selectively bound to these molecules, wherein light waves can be coupled into the substrate and can be guided through this, and wherein the substrate is a foil element made of a transparent material in which a coupling structure for coupling the light waves is integrally formed and in which the coupled light waves can be guided.

This invention relates to a device for optical detection of substancesin a liquid or gaseous medium, in particular to a biochip or amicroarray. Moreover, the present invention relates to a method formanufacturing a substrate for molecules for detection of the substancesfor use in this device. The present invention furthermore relates aswell to a method and a device for spatially-resolved detection ofchemical reactions on a surface (of the substrate).

Chemical reactions near the surface are particularly used for detectionof analytes in liquid samples. For example, so-called probes (molecules)are immobilized, i.e., chemically bound, for this purpose at the surfaceof a substrate. Probes are molecules that bind the analytes that are tobe detected. This binding should take place largely selectively, so thatthe binding event makes it possible to conclude the presence of theanalyte that is to be detected (the substance to be detected).

By producing many probes on the (measurement) surface of the substrateas measuring points in the form of a so-called microarray, it ispossible to carry out many detection reactions at the same time on asmall surface by binding different types of probes at different pointsof the surface.

In many applications, it is advantageous to carry out the respectivedetection in the presence of the probe in this connection. If there isonly a small quantity of probe volume available for this purpose, it isalso possible to use microfluid elements on the surface, in order tobring the probe into contact with the surface.

The analytes that are to be deposited on the surface can be, e.g., DNAmolecules, preferably DNA single strands. In this case, for example, DNAmolecules are also bound to the surface as probes. These analytemolecules (i.e., the substances to be detected) can bind to these probesby means of a so-called hybridisation reaction, if the sequences of thenucleobases are complementary. In this way, selective registration ofcertain DNA sequences at a point of the microarray is made possible.

A further possibility is found in immobilising antibodies as probes atthe surface, where these antibodies specifically bind the specificantigen.

A method for reading out a measurement array (=detection of theanalyte(s)) should be able to detect very small quantities of theanalytes (i.e., the substance that is to be detected) after these havebeen bound to the probes. At the same time, the detection should also bemade possible in a spatially-resolved manner, so that simultaneousanalysis of a plurality of contents is possible.

Applications of such a (detection) method can be found, e.g., in medicaldiagnostics, in which body fluids, such as whole blood, serum, plasma,saliva, or urine are used as samples to be examined. In some cases, thesample must then be pre-treated. Moreover, simultaneous analysis of aplurality of parameters is necessary for reliable diagnosis of certainsymptoms.

Other applications are the analysis of foodstuffs and water, e.g., withregard to pathogenic germs, as well as in forensics.

In principle, electric, electrochemical and optical detection principlescan be used for the detection of the binding of the analyte molecules(i.e., the substances to be detected) to the probes immobilised at thesurface. In addition, there are gravimetric and calorimetric methods.

One of the electrical methods is based on the production of strongelectric fields on the surface by means of microelectron arrays withvery tight contact spacing. With the help of further reagents, there isa redox reaction on the surface, which generates an electric signal.

The optical methods are very predominantly fluorescence-opticaldetection methods. Fluorescence-optical detection requires a fluorescentmolecule, because the analyte molecules that are to be detected are notthemselves fluorescent, as a rule. The fluorescent dyes are thendetected with a suitable optical system.

This labelling can be achieved by means of labelling the analyte itselfwith the dye before performing the binding reaction on the surface.

Alternatively, it is also possible to place anotherfluorescence-labelled substance on the surface after binding the analyteto the respective probe, whereby this substance in turn binds only withthe already bound analyte molecules. This is the process used, forexample, in the case of so-called sandwich assays, in which twoantibodies (a “captured” antibody and a “labelled” antibody that isadded later) are used.

It is furthermore possible to perform a so-called competitive test, inwhich a labelled substance is used that competes against analytes tobind to the probe.

This fundamental procedure for fluorescence-optical detection by meansof a sandwich assay is shown schematically in FIGS. 1A to 1C, whereby inFIG. 1A the surface 1 is shown with antibodies 2 as probes. As is shownin FIG. 1B, the corresponding antigens (the substance to be examined) 3deposit on these antibodies 2. The addition of a second antibody 4 isshown in FIG. 1C. This second antibody 4 is labelled with a fluorescentdye 5. The second, labelled antibody now deposits on the substance thatis to be detected (the antigen) 3.

Methods for optical readout of fluorescent microarrays (biochips) areshown schematically in FIG. 2. As far as known, in most cases, after thereaction with the sample, such biochips are rinsed, dried and then readout in an optical system for spatially-resolved detection of thefluorescent labels. In this process, an image of the chip is createdthat represents the distribution of the fluorescence intensity on thesurface of the biochip. These images are often further evaluated withmethods for image processing. At the same time, the fluorescenceintensity integrated over a measurement point is typically evaluatedafter discounting the background (background radiation).

To determine the fluorescence intensity, laser scanners are mainly usedin which a focus of a laser 6 is moved across the surface 1. This laserfocus is used to excite the fluorescence depending on the position. Thefluorescent light is typically received with a photomultiplier 7 asdetector. The scan process accordingly takes place either by means of arapid movement of the biochip in two directions in space (“movingstage”), as shown schematically in FIG. 2A, or by rapid movement of apart of the optical system in the excitation beam path (“flyingoptics”), as shown schematically in FIG. 2B, or by a rotating scannermirror, which is mounted in the excitation beam path in front of thefocussing optics (“pre-objective scan”), as shown schematically in FIG.2C.

In addition to laser scanners, imaging systems are also used in whichthe surface of the biochip or a part thereof is illuminated, as shownschematically in FIG. 2D. In this case, the radiation produced by alight source 8 is projected on to the surface 1 of the substrate and theresulting fluorescent radiation is recorded with a camera, particularlya CCD camera.

In the detection methods described in FIGS. 2A to 2D, the upper or lowerside of the biochip is always illuminated. If, however, the measurementshould be made in the presence of the sample, the fluorescent molecules(fluorochromes) that are not bound are also excited to fluorescence inthe solution located above the biochip. This increases the backgroundradiation, which considerably increases the detection limit of themeasurement system and so worsens the measurement precision.

One possibility for avoiding this problem would be in the use of TIRFtechnology (TIRF=total internal reflection fluorescence), which is shownin FIG. 3. In this arrangement, laser light L is created with a laserdiode 10 with linear optics, coupled into the biochip 20 and guidedalong the biochip 20. Excitation of the fluorescence is effected via theevanescent field of the coupled laser beam light, namely exclusivelywithin a very small distance of the biochip surface (approximately50-300 nm, depending on the optical arrangement).

The biochip needed when TIRF technology is used can be realised bypreparing standard object slides in such a way that it is possible tocouple light in through an edge of the glass of the object slide. Thisprepared edge must additionally be polished so that the light can becoupled into the biochip without being scattered. Such object slidesthat are suitable for appropriate preparation are typicallyapproximately 1 mm thick, so that the laser can very efficiently becoupled into the polished edge.

It would, however, be advantageous if the thickness of the substratewere considerably smaller. In this case, the efficiency of thefluorescence excitation would be considerably greater. The efficiency ofthe fluorescence excitation here can be estimated by calculating thenumber of reflections at the biochip surface per path unit.

As the thickness of the chip decreases, the number of reflectionsincreases at a constant beam angle relative to the chip surface,whereby, however, the light intensity drops considerably after a shortdistance as the light is directed in the biochip. The beam angle, on theother hand, is determined by the total reflection critical angle, fromwhich point there is no more total reflection. If the coupling angle tothe normal at the surface is considerably larger than this criticalangle, the evanescent field at the surface reduces sharply, as a resultof which the efficiency of the fluorescence excitation is worsened.

Using considerably thinner glass substrates for the biochip fails,however, because coupling the light at the prepared edge is thenconsiderably more difficult. At glass thicknesses less than 500 μm, thepolishing and general handling of the biochip are also considerably moredifficult.

To avoid this disadvantage, it could be attempted to form the endsurfaces in such a way that good coupling efficiency is achieved evenwith small thicknesses of the glass substrate that is used. For example,lenticular structures could be formed, with which the light is focusedinto the glass substrate. Such structures are, however, difficult tomanufacture.

A further disadvantage of the “frontal” coupling into the glasssubstrate is seen in the fact that sealing a sample container placed onthe glass substrate or a flow cell interferes with the lighttransmission at this cell and produces extra losses.

It has already been suggested that the thickness of the waveguide befurther reduced by applying a waveguide to a substrate as a thincoating, as is shown in FIG. 4, which shows a thin-film waveguide withgrating coupling. In this case, the light beam L is again coupled intothe waveguide 30 at the front via the diffraction grating 40.

Using such a solution, waveguide thicknesses down to as little asapproximately 150 nm could be used, which considerably increases theintensity of the evanescence field. It is, however, more difficult tocouple the light in this case. As a rule, diffraction gratings are usedto realise the coupling, whereby these gratings are etched into thesurface of the glass substrate. Because of the small structure size ofthe gratings (period length approximately 300 to 400 nm), thisprocessing step is a very expensive process that requires clean roomequipment. Moreover, considerable scattering of the light guided in thewaveguide has been observed with these diffraction gratings, even atvery low levels of surface roughness on the waveguide surface (a fewnm). This causes the background of the received image to become moreprominent if the fluorescent light is not filtered perfectly. Becausethe noise of the background image essentially determines the detectionlimit, the actual advantage of the higher proportion of evanescencefield can no longer be fully utilised.

One object of the present invention is to avoid the disadvantages of theTIRF method discussed in the preceding, particularly for reading outbiochips, namely the complicated process steps in the manufacture ofbiochips that are necessary in order to couple the light into thewaveguide (edge polishing or structuring of diffraction gratings),because these two steps make biochip production more expensive to such adegree that the biochip is not competitive on the market.

The aforementioned object is solved according to the invention by meansof a device for optical detection of substances in a liquid or gaseousmedium with a substrate with molecules for detecting the substances tobe detected, that are immobilised on a surface of the substrate or inthe substrate, and to which the substances that are to be detected canselectively be bound, whereby light waves can be coupled into thesubstrate and guided through this, and whereby the substrate is a foilelement made of a transparent material, in which a coupling structurefor coupling the light waves is integrally formed and in which thecoupled light waves can be guided.

At the same time, the coupling structure can already be formed duringthe forming step of the foil element itself, on the surface on the foilelement in a step together with the formation of the foil element.

The foil element can furthermore be manufactured from a liquid medium bymeans of stamping, rolling, casting or hardening.

Furthermore, the coupling structure can already be formed in the mouldused for stamping, rolling or injection moulding, so that with thismould, it is possible to manufacture the coupling structure in one stepsimultaneously with the manufacture of the foil element, andparticularly of its surface.

This device can furthermore have a flow cell for the medium that is tobe examined, whereby this flow cell forms a measuring area with thesurface of the foil element, whereby the coupling structure is arrangedin the area covered by the flow cell.

The molecules for detecting the substances that are to be detected canbe probes made of biological and/or biochemical molecules, such asantibody molecules and/or DNA molecules and/or DNA single strands and/orRNA molecules and/or RNA single strands, that are immobilised on thesurface of the foil element or in the foil element.

The present device can additionally have a multiplicity of (such)molecules for detecting the substances that are to be detected, wherebythese molecules are immobilised on the surface of the foil element or inthe foil element, and form a readout field (microarray) with amultiplicity of measuring points for spatially-resolved detection of thesubstances to be detected.

The foil element can furthermore have a homogenising area that isarranged in the beam path downstream of the coupling structure and ameasuring point that is arranged upstream, particularly before thereadout field, so that the light waves coupled into the foil element viathe coupling structure are distributed homogenously before reaching themeasuring point.

Furthermore, an element that homogenises the light waves, particularly adiffractive optical element, such as a grating structure, can also beprovided in the beam path downstream of the coupling structure andupstream of the measuring point.

The coupling structure can moreover have a curvature, comparable to acylinder lens or a round form, in order to achieve homogenousdistribution of the light sources that are coupled into the foil elementvia the coupling structure.

The coupling structure can moreover be a refractive optical element,such as a prism or a grating or a structure with a trapezoidal orrectangular cross-section.

The coupling structure can likewise be a diffractive optical element.

A thickness of the foil element can lie in the range from 10 μm to 1,000μm.

A thickness of the foil element can be selected in such a way that thefoil element has a flexibility, whereby the foil thickness particularlycan amount to around 100 μm.

During the shaping process, the foil element can be shaped with athicker area, particularly in the form of a frame that increases themechanical stability of the foil element.

The device can moreover have a polymer cartridge into which the foilelement is integrated, whereby said polymer cartridge has an injectionport for the medium that is to be examined, reagent containers, fluidcanals for transporting the medium and the reagents, and devices formoving the medium and the reagents.

The device can furthermore have excitation optics for generating thelight waves, particularly for exciting a label used for opticaldetection, such as a fluorescent dye, or for producing a change incolour at the surface or in the foil element depending on the mediumthat is to be examined.

The device can furthermore have a device for changing a relativeposition of the excitation optics to the coupling structure, with whicha coupling angle can be selected in such a way that it roughlycorresponds to the total reflection angle that results with therefractive index of the medium adjacent to the foil element.

The device can furthermore have a decoupling structure, formed into thefoil element, for decoupling the light waves, whereby this decouplingstructure is formed in the forming step of the foil element at thesurface of the foil element in one step, together with the formation ofthe foil element itself.

The decoupling structure can be a refractive optical element such as aprism or a grating or a structure with a trapezoidal or rectangularcross-section, or a diffractive optical element.

A detector can be arranged in the beam path, downstream of thisdecoupling structure in the beam path, whereby the light waves decoupledout of the decoupling structure can be detected with this detector,particularly for optimisation of the beam position and/or fordetermining the scattered light of the coupled light waves.

The detector can be provided for detection of an intensity of the lightwaves at the decoupling structure for determining an adsorption of thelight waves guided in the foil element and for determining their change.

The device can furthermore have focusing optics with which opticalcharacteristics, particularly fluorescence characteristics or colours,of substances or labels bound at the surface or in the foil element canbe measured.

The foil element can be made from an optically transparent plastic madeof organic polymers, such as polymethyl methacrylate, polystyrene,polycarbonate, PEG and polyolefins or from copolymers, such as COC.

The foil element can furthermore be made of a glass, which ismanufactured by means of hot stamping.

From the point of view of the method, the object according to theinvention is solved by a method for manufacturing a substrate formolecules for the detection of substances in a gaseous or liquid mediumfor use in the present device, whereby the substances that are to bedetected can largely be selective bound to the probes, and whereby thesubstrate is manufactured as a foil made of a transparent material bymeans of stamping, rolling, casting, or hardening a fluid medium in amould in such a way that both the surface and a coupling structure forcoupling light waves are formed in one manufacturing step.

Plastic foils could be used as the base material for the substrate,whereby these plastic foils are processed with a mould at a raisedtemperature, whereby particularly metal elements processed withmicro-millers or silicon wafers with structures introduced by means ofanisotropic etching or rolling can be used as moulds.

The substrate can also be manufactured by means of casting, particularlyinjection moulding.

Alternatively, the substrate can be manufactured from a liquid medium byhardening the medium in a mould. The hardening process can be triggeredby means of UV radiation with special media suitable for this purpose(plastics that can be hardened by UV).

The present invention is explained in more detail in the following usingpreferred embodiments in connection with the associated drawings. Shownare:

FIG. 1A to 1C production of a sandwich assay,

FIG. 2A to 2D known detection methods for the readout of fluorescentbiochips,

FIG. 3 a TIRF arrangement with planar glass substrate,

FIG. 4 a thin-film waveguide with grating coupling,

FIG. 5 a foil sensor according to an embodiment with a substrate elementwith coupling structure,

FIG. 6 a foil with prism-shaped coupling and decoupling structures forforming the present foil sensor and

FIG. 7 a to FIG. 7 d additional embodiments of the substrate elementwith various coupling structures.

FIG. 5 shows a foil sensor as a biochip (microarray) made of a thinpolymer foil, wherein the excitation light is guided in the polymer foil100. The excitation light L1 is produced via a laser diode with linearoptics 101. The excitation light L1 is coupled by means of an opticalstructure 102, which is called the coupling structure in the following.This coupling structure 102 is introduced into the surface of the foiltogether with the shaping process of the foil itself.

The shaping process can be a stamping process, for example. Extremelysmooth surfaces can be produced with a stamping process without complexadditional steps, whereby the light is reflected at these surfaces withonly negligible scattering at this surface, so that the light is guidedin the polymer foil practically without loss and little backgroundradiation is produced.

A rolling process or a casting process, particularly an injectionmoulding process, can also be used. It is also conceivable for thepolymer foil to be manufactured by hardening a liquid medium.

All of these various manufacturing processes have in common that at anyrate, the coupling structure is produced at the surface of the foilelement in the forming step of the foil element itself, together withthe formation of the surface of the foil element.

In the case of stamping or casting (injection moulding), the structurefor coupling the light is defined by means of the mould used for thestamping and injection moulding. This process can be carried out veryeconomically when there a large number of pieces are produced, so thatthe biochip costs are extremely low.

The coupling structure 102 is not produced in the edge area of the foil100 in this embodiment. Instead, the coupling structure 102 is producedin an area of the foil 100 that is covered by a flow cell 103, which isshown in FIG. 5 only schematically and without taking into considerationthe actual size relationships. In this way, the sealing of the flow cell103, meaning, e.g., of the sample container, does not interfere with thelight guidance in the foil element 100. The manufacture of the thinfoils is furthermore considerably simplified if the edge area of thesubstrate (i.e., the end of the foil structure) does not have to bespecially shaped, so that the foil element 100 can be stamped out of thematerial with the already formed coupling structure 102 in a simplemanner after the shaping process.

The coupling structure 102 can, for example, be formed as a prismstructure, as is schematically suggested in FIG. 5. Alternatively,however, other shapes can also be used here, such as rectangularcross-sections or round shapes, for example.

Rounded shapes, similar to a cylinder lens, bring about a focussing ofthe light into the foil. Important here is that the coupling/decouplingstructure have one or more surfaces whose orientation differs from thefoil surface.

A plurality of structures can also be combined, as shown in FIG. 7 b.This arrangement allows coupling over a stipulated beam cross-section inthe case of structure heights that are considerably smaller than asingle structure with larger dimensions (cf. FIG. 7 a). Thecoupling/decoupling structures can also be formed as a depression, asshown in FIG. 7 c. If the dimensions of these structures are stillconsiderably larger than the wavelength of the light, the deflection ofthe beam into the foil is essentially brought about by the refraction ofthe light at the surface of the structures.

Grating structures are also possible because very fine structures ingood quality can also be transferred to the polymer surface with thecited manufacturing methods. In this case, the structures of thecoupling/decoupling element are so small that the deflection of thelight is essentially achieved by the light diffraction (cf. FIG. 7 d).

FIG. 6 shows a usable foil with a coupling structure 102 and adecoupling structure 104 (which will be described in more detail in thefollowing), wherein the coupling structure 102 and the decouplingstructure 104 are prism-shaped coupling/decoupling structures. FIG. 6shows both a top view in FIG. 6 a and a cross-section along the cut A-A.Indications of the dimensions in mm are also shown in FIG. 6 by way ofexample, whereby these describe an implemented embodiment of the foilsensor.

The foil thickness is typically in the range from 10 μm to 1,000 μm (130μm in the present embodiment). The foil sensor correspondingly has acertain flexibility, by means of which the foil sensor can be adapted tovarious geometric shapes.

In the case of very thin foils, a thicker outer area, roughly in theshape of a frame, is also formed during the shaping process, wherebythis thicker outer area makes possible increased mechanical stability,which is helpful for handling the foils.

Foils of the kind shown can be integrated into a polymer cartridge thatincludes further functions. Polymer cartridges of this kind canparticularly have an injection port for the sample that is to beexamined, reagent containers, fluid canals for transporting the media(sample, reagents) and devices for moving the media in the cartridge.

With a polymer cartridge into which the foil sensor has already beenintegrated, complete solutions, e.g., for on-the-spot diagnosis (POCT:point of care testing) can also be realised, which are very easy tohandle and which can be produced as disposable articles.

The excitation optics 101 can be realised with a multiplicity ofdifferent light sources. Consequently, laser sources, LEDs, gasdischarge tubes or other light sources can be used. Lasers areadvantageous, however, because of the good beam quality. At the sametime, semiconductor lasers are advantageous for cost reasons as long asthe emission wavelength is suitable for exciting the indicator (dye)used in the respective case.

The light beam is collimated and, where appropriate, diverged after itis produced.

Then cylindrical optics are used to produce a line that is targeted atthe coupling prism (102).

The corresponding coupling angle here is selected so that it roughlycorresponds to the total reflection angle that results with therefractive index of the adjacent medium.

Because the foils or cartridges are not generally placed into acorresponding device with the necessary positioning accuracy, automaticmovement of the beam in a direction perpendicular to the line producedby the cylindrical optics is provided according to the presentembodiment. The position is changed with this automatic positioningdevice in such a way that maximum coupling efficiency is achieved.

Final optimisation of the beam position takes place by measurement,either at a second coupling/decoupling point (i.e., the decouplingstructure 104) or by determining the scattered light of the lightguidance.

Homogeneity of the excitation is a crucial influence that guaranteescomparability of the measurement at different points on the chip. As arule, homogeneity is guaranteed in the direction perpendicular to thebeam propagation by appropriate selection of the divergence and beamshaping optics. Modulation of the light intensity is initially noted inthe direction of the beam directly after the coupling, however. Becauseof the focusing on to the coupling prism 102, however, after a certaindistance (usually 5 to 10 mm, depending on the specific depictions ofthe foil sensor) from the coupling prism, the distribution is veryhomogenous. Accordingly, at least one homogenisation area is providedfollowing the coupling optics 102.

As already explained, the optimisation of the light coupling can also bedone automatically, as a rule, by readjusting the positioning of thebeam on to the prism. For this purpose, a detector is arranged behindthe decoupling optics (the decoupling prism 104), whereby the lightdecoupled from this prism is detected by this detector. If thisintensity is optimised, the intensity of the light guided in the foil isalso optimised.

The detection of the substances that are to be detected is done withfocusing optics 104, which ideally are combined with spectral filteringof the light. By means of this filtering, the scattered excitation lightcan be removed from the detector beam input. In addition, it is alsopossible to reduce the background, which is produced by the fluorescenceof the foil itself, among other causes.

The detection can be done by means of a very wide range ofspatially-resolved detectors. A camera 105 is used according to theembodiment shown in FIG. 5. The sensitivity of this detection device 105is an important point, because even very low concentrations offluorescent labels (fluorochromes) must still be detected at thesurface. Suitable for this are CCD cameras, which can be used withoutcooling or with cooling of the CCD chip. By cooling the CCD chip, thedark current is reduced at long integration times, as a result of whichthe registration of very low light intensities is made possible.

The entire device is regulated by a PC or another microcontroller. Theimage capture and processing are also done essentially automatically bymeans of the PC or microcontroller.

In addition to the detection of the fluorescent light, the guided lightcan be decoupled again by the decoupling structure 104, as a result ofwhich further measurement functions can be realised.

Materials that can be considered for the foils are variousoptically-transparent plastics, such as polymethyl methacrylate,polystyrene, polycarbonate, PEG and polyolefins. Copolymers, such asCOC, for example, can also be considered. In addition to the organicpolymers, glasses which can be shaped by hot stamping can also beconsidered.

The manufacture of foils with the integrated coupling/decouplingstructures 102, 104 can, as already explained at the beginning, berealised with various shaping methods for plastics.

Stamping of the foils uses as a base material foils that are processedwith the mould at a raised temperature. Metal elements that have beenprocessed with micro-millers, for example, can be used as moulds forthis. Alternatively, silicon wafers in which structures have beenintroduced by means of anisotropic etching, e.g., with KOH, can also beused. This manner of manufacturing the foil sensors is advantageous inthat the surfaces have very low levels of surface roughness. Whensilicon wafers are used, however, the usable angle of the createdsurfaces is restricted to certain values, which are determined by theparticular crystal structure of the silicon and the crystal cut used. Ifthe structure depths are small (e.g., when coupling/decoupling gratesare used), photolithographically structured surfaces with subsequentisotropic etching are also advantageous.

Additional possible methods for manufacturing the polymer structure ofthe foil element are rolling and stamping with UV hardening of thepolymer. Injection moulding is likewise usable.

This description discloses an optical system, in particular fordetection of fluorescent molecules at a surface of a thin polymer foil,into which, with the help of special coupling/decoupling structures,light is coupled and guided. At the same time, the coupling/decouplingstructure is produced in the surface of the foils, not on the edge ofthe foil. An additional coupling/decoupling structure can serve todecouple the light, as a result of which an intensity in the foil(coupling efficiency) can be optimised.

Coupling of the light is preferably done in a limited angle spectruminstead of a parallel light beam which has only a single beam angle. Inthis way, the intensity distribution in the foil is homogenised after arun-in path. In the case of a parallel input beam, the individualreflections of the light would appear light at the two surfaces, whilethe areas between the reflection points would not be illuminated. Inthis embodiment, the foil sensor has an area after the couplingstructure in which there is no detection, and whereby this area servesonly to homogenise the intensity distribution.

Detection with the foil sensor under consideration can take placed as afunction of the location.

The cross-sectional area of the coupling/decoupling structure cancorrespond to a prism.

The coupling/decoupling structure can likewise be another refractingoptical element, such as a structure with a trapezoidal or rectangularstructure, for example.

In the cross-section, the coupling/decoupling structure can also bordera circle, such as have a semi-circle, for example. Thecoupling/decoupling structure can likewise be a diffractive element.

One thickness of the foil can amount to between 10 μm and 1,000 μm.

The detection reactions can be DNA-DNA hybridizations, immune reactionsor other reactions that lead to a change in the fluorescencecharacteristics at the surface on one surface.

Instead of the measurement of fluorescence characteristics of the mediabound at the surface, the absorption of the guided light and its changecan be determined, by means of detecting the intensity at the output ofthe decoupling structure.

The fluorescence characteristics that are to be detected can also besuch that are to be found in the foil, instead of at the surface of thefoil. In this case, the foil itself has sensor characteristics andabsorbs substances from the surroundings.

The absorption of molecules at the foil surface can also be replaced bythe absorption of the light in the foil itself.

1. Device for optical detection of substances in a liquid or gaseousmedium, with a substrate with molecules for detecting the substancesthat are to be detected, said molecules being immobilised at a surfaceof the substrate or in the substrate and to which the substances thatare to be detected can essentially be selectively bound, wherein lightwaves can be coupled into the substrate and can be guided through it,wherein the substrate is a foil element made of a transparent materialin which a coupling structure for coupling the light waves is integrallyformed and in which the coupled light waves can be guided.
 2. Deviceaccording to claim 1, wherein the coupling structure is formed at thesurface of the foil element during the forming step of the foil elementin one step, together with the formation of the foil element itself. 3.Device according to claim 2, wherein the foil element is manufacturedfrom a liquid medium by stamping, rolling, casting or hardening. 4.Device according to claim 3, wherein the coupling structure is formed inthe mould used during stamping, rolling or injection moulding in such away that the coupling structure can be manufactured with this mould inone step simultaneously with the manufacture of the foil element, andparticularly its surface.
 5. Device for optical detection of substancesin a liquid or gaseous medium, with a substrate with molecules fordetecting the substances that are to be detected, said molecules beingimmobilised at a surface of the substrate or in the substrate and towhich the substances that are to be detected can essentially beselectively bound, wherein light waves can be coupled into the substrateand can be guided through it, wherein the substrate is a foil elementmade of a transparent material in which a coupling structure forcoupling the light waves is integrally formed and in which the coupledlight waves can be guided and comprising a flow cell for the medium tobe examined, which forms a measurement area with the surface of the foilelement, wherein the coupling structure is arranged in the area coveredby the flow cell.
 6. Device according to claim 5, wherein the moleculesfor detecting the substances that are to be detected are probes made ofbiological and/or biochemical molecules, such as antibody moleculesand/or DNA molecules and/or DNA single strands and/or RNA moleculesand/or RNA single strands, which are immobilised at the surface of thefoil element or in the foil element.
 7. Device according to claims 1,comprising a multiplicity of molecules for detecting the substances thatare to be detected, wherein these molecules are immobilised on thesurface of the foil element or in the foil element and form a readoutfield with a multiplicity of measurement points for spatially-resolveddetection of the substances that are to be detected.
 8. Device accordingto claim 1, wherein the foil element has an homogenizing area that isarranged in the beam path downstream of the coupling structure andupstream of a measurement point, particularly before the readout field,so that the light waves coupled into the foil element via the couplingstructure have a homogenous depression before reaching the measurementpoint.
 9. Device according to claims 1, wherein an element thathomogenizes the light waves, particularly a diffractive optical elementsuch as a grating structure, is provided in the beam path downstream ofthe coupling structure and upstream of the measurement point.
 10. Deviceaccording to claim 9, wherein the coupling structure has a curvature,comparable to a cylinder lens or a round form, in order to achievehomogenous distribution of the light waves that are coupled into thefoil element via the coupling structure.
 11. Device according to claim10, wherein the coupling structure is a refractive optical element, suchas a prism or a grating or a structure with a trapezoidal or rectangularcross-section.
 12. Device according to claim 10, wherein the couplingstructure is a diffractive optical element.
 13. Device according toclaim 1, wherein a thickness of the foil element lies in the range from10 μm to 1,000 μm.
 14. Device according to claim 13, wherein a thicknessof the foil element is selected in such a way that the foil element hasa flexibility, wherein the foil thickness is particularly around 100 μm.15. Device according to claim 14, wherein during the forming process,the foil element is formed with a thicker outer area, particularly inthe form of a frame, which increases the mechanical stability of thefoil element.
 16. Device according to claim 5, wherein a polymercartridge into which the foil element is integrated, wherein thispolymer cartridge has an injection port for the medium that is to beexamined, reagent containers, fluid canals for transporting the mediumand reagents, and devices for moving the medium and the reagents. 17.Device for optical detection of substances in a liquid or gaseousmedium, with a substrate with molecules for detecting the substancesthat are to be detected, said molecules being immobilised at a surfaceof the substrate or in the substrate and to which the substances thatare to be detected can essentially be selectively bound, wherein lightwaves can be coupled into the substrate and can be guided through it,wherein the substrate is a foil element made of a transparent materialin which a coupling structure for coupling the light waves is integrallyformed and in which the coupled light waves can be guided and comprisingexcitation optics for producing light waves, particularly for exciting alabel used for optical detection, such as a fluorescent dye, or forproducing a colour change at the surface or in the foil elementdepending on the medium to be examined.
 18. Device according to claim17, comprising a device for changing a relative position of excitationoptics to the coupling structure, with which a coupling angle can beselected in such a way that it roughly corresponds to the totalreflection angle, which results with the refractive index of the mediumadjacent to the foil element.
 19. Device according to claim 18,comprising a decoupling structure formed into the foil element, whereinthis decoupling structure is for decoupling the light waves and isformed at the surface of the foil element during the forming step of thefoil element in one step, together with the formation of the foilelement itself.
 20. Device according to claim 19, wherein the decouplingstructure is a refractive optical element, such as a prism or a gratingor a structure with a trapezoidal or rectangular cross-section, or thatthe decoupling structure is a diffractive optical element.
 21. Deviceaccording to claim 20, wherein a detector is arranged in the beam pathdownstream of the decoupling structure in the beam path, wherein thelight waves decoupled from the decoupling structure can be detected bythis detector, particularly for optimising the beam position and/or fordetermining the scattered light of the coupled light waves.
 22. Deviceaccording to one of the claim 21, wherein the detector for detection ofan intensity of the light waves is provided at the decoupling structurefor determining absorption of the light waves guided in the foil elementand their change.
 23. Device according to claim 6, comprising focusingoptics with which optical characteristics, particularly fluorescencecharacteristics or colours, of substances or labels bound at the surfaceor in the foil element can be measured.
 24. Device according to claim 1,wherein the foil element is made of an optically transparent plasticmade of organic polymers, such as polymethyl methacrylate, polystyrene,polycarbonate, PEG and polyolefins, or from copolymers, such as COC. 25.Device according to claim 23, wherein the foil element is made of aglass that is manufactured by hot stamping.
 26. Method for manufacturinga substrate for molecules for the detection of substances in a gaseousor liquid medium, wherein the substances that are to be detected canlargely be selectively bound to the probes, wherein the substrate ismanufactured as a foil from a transparent material by pressing, rolling,casting or hardening a liquid medium in a mould in such a way that boththe surface and a coupling structure for coupling light waves are formedin one manufacturing step.
 27. Method according to claim 26, whereinplastic foils are used as the base materials for the substrate, whereinthese base materials are processed with a mould at a raised temperatureand wherein metal elements processed particularly with micro-millers orsilicon wafers with structures introduced by means of anisotropicetching or rolling are used as moulds.
 28. Method according to claim 26,wherein the substrate is manufactured by casting, particularly byinjection moulding.
 29. Method according to claim 28, wherein thehardening process is produced in a mould by means of UV radiation.